This term is very loosely applied to various substances which differ considerably from one another. These may be classed as follows : - 1. Compounds of hydraulic lime, formerly much used for external covering to walls. 2. Mixtures of lime, plaster, and other materials for forming smooth surfaces on internal walls, chiefly those intended to be painted. 3. All sorts of calcareous cements and plasters used for covering walls.

These latter have been described under their several heads.

Common Stucco consists of three parts clean sharp sand to one part of hydraulic lime.

It was much used at one time as an external covering for outside walls, but has to a great extent been superseded by cements of recent introduction.

The method of applying this and the other compositions mentioned below is described at p. 406, Part II.

Trowelled Stucco is used for surfaces intended to be painted, and is com-" posed of two-thirds fine stuff (without hair) and one-third very fine clean sand.

Bastard Stucco is of the same composition as trowelled stucco, with the addition of a little hair.

Rough Stucco contains a larger proportion of sand, which should, moreover, be of a coarser grit. The surface is roughened as described at page 406, Part II., to give it an appearance like that of stone.

Artificial Marbles may be produced by skilful workmen by working colours in with almost any of the white cements or rather plasters mentioned at pages 242, 243.

Certain processes for imitating marbles are, however, known by distinctive names, and one or two of the more important of these will now be briefly noticed.

Scagliola is a coating applied to walls, columns, etc., to imitate marble. It is made of plaster of Paris, mixed with various colouring matters dissolved in glue or isinglass; also with fragments of alabaster or coloured cement interspersed through the body of the plaster.

The method of applying and finishing this material is described at page 410, Part II.

Marezzo Marble is also a kind of plaster made to imitate marble.

A sheet of plate-glass is first procured, upon which are placed threads of floss silk, which have been dipped into the veining colours previously mixed to a semi-fluid state with plaster of Paris. Upon the experience and skill of the workman in placing this coloured silk the success of the material produced depends. When the various tints and shades required have been put on the glass, the body colour of the marble to be imitated is put on by hand. At this stage the silk is withdrawn, and leaves behind sufficient of the colouring matter with which it was saturated to form the veinings and markings of the marble. Dry plaster of Paris is now sprinkled over to take up the excess of moisture, and to give the plaster the proper consistence. A canvas backing is applied to strengthen the thin coat of plaster, which "is followed by cement to any desired thickness; the slab is then removed from, the glass and polished.

"Imitation marble of this description is employed for pilasters and other ornamental work, and is now used by Mr. George Jennings in the manufacture of a variety of articles."

"The basis of Marezzo marble, as well as of Scagliola, being plaster of Paris, neither of them is capable of bearing exposure to the weather."1

"The Artificial Marble now manufactured in London is made on the same principle as the Marezzo, but differs from it in the character of the cement used. A less expensive table is also substituted for the plate glass, and the canvas backing is altogether omitted."1

Other artificial marbles are described at page 76.